In years past, back in the days of the GeForce 4, the MX line was the lower end alternative to the venerable Ti line. NVIDIA has already brought back the Ti name in the 500 and 600 series, so why not the MX line too? This time, however, the MX moniker is being attached to high end mobile GPUs, with the fastest being the GeForce GTX 680MX. That version features the full 1536 CUDA core count, unlike the 680M and its 1344 count. The core clock on the 680MX is at 720MHz, just like the 680M, but the memory speed has jumped to 5000MHz from 3600MHz. The 675MX features similar improvements, with 960 CUDA cores (instead of 384 on the 675M), a 2100MHz memory clock (up from 1500MHz), but a small reduction in core clock to 600MHz from 620. NVIDIA's 670MX is likewise boosted across the CUDA cores and memory clocks.
Currently, there aren't any laptops running the new mobile MX line, but NVIDIA says the 680MX and 675MX are available as options on the new 27" Apple iMac. That won't be shipping until the middle of December though, so hopefully some laptops or other all-in-one systems get tricked out with the new, more powerful GeForce MX.